Method and system for metal-coating

ABSTRACT

The invention relates to a method and to a system for metal-coating at least one surface of a workpiece, in which before coating, a surface structure with peaks and troughs in the surface to be coated is detected by means of a measuring apparatus, the coating is carried out by means of at least one deposition apparatus, which is moved relative to the surface and applies coating material in the process, and the deposition apparatus is controlled by a control apparatus on the basis of the detected surface structure, wherein more material is applied in the region of troughs and less material is applied in the region of peaks.

The invention relates to a method for metal-coating at least one surface of a workpiece according to claim 1.

The invention further relates to a system for metal-coating at least one surface of a workpiece according to claim 13.

Systems and methods for metal-coating of workpieces using a coating device, by means of which a metal coating is applied to a workpiece surface, have been known for long-time. Coating devices of this kind are used in the coating of cylinder bores in engine blocks, for example, with a plasma spraying method, a thermal spraying method or another metal-coating method being used.

From EP 3 048 181 B1 of the applicant, a method and a system for metal-coating of workpieces is known, in which an engine block comprising cylinder bores to be coated is arranged on a rotary table, by means of which the workpiece can be swiveled between a loading station and a processing station. In this process, the engine block is received in the loading station, with the cylinder bores being measured using a measuring apparatus before being coated. In so doing, a surface structure can be recorded. The engine block is then swiveled into the coating position, with a metal coating being applied to the cylindrical bore surfaces by means of plasma spraying. At the same time, when swiveling the engine block into the coating position, an engine block that has finished being coated is swiveled back into the loading position. In the process, the coated engine block is measured using the same measuring apparatus before being unloaded from the loading station. By comparing the surface structure before and after coating, the layer thickness and the layer-thickness contour can be precisely determined.

The invention is based on the object to provide a method and a system for metal-coating of workpieces, by means of which a coating having a desired surface contour can be applied with particularly high efficiency.

According to the invention, the object is solved both by a method having the features of claim 1 and by a system having the features of claim 13. Preferred embodiments of the invention are set out in the dependent claims.

In the method according to the invention for metal-coating at least one surface of a workpiece, it is provided, before coating, for a surface structure with peaks and troughs in the surface to be coated to be detected by means of a measuring apparatus, for the coating to be carried out by means of at least one deposition apparatus, which is moved relative to the surface and applies coating material in the process, and for the deposition apparatus to be controlled by a control apparatus on the basis of the detected surface structure, wherein more material is applied in the region of troughs and less material is applied in the region of peaks.

The invention is based on the knowledge that workpieces to be coated may have a macroscopically rough surface structure comprising peaks and troughs depending on the type of pre-processing, which may include casting, punching, forging and in particular material-removing machining. When applying a coating with high coating accuracy, a rough surface structure of this kind may substantially still be present or may develop in a more pronounced manner on the surface structure of the coated surface. In order to counteract this, according to the invention the deposition of the coating is controlled by a control apparatus depending on the detected values for the surface structure. In this process, the control takes place such that, during the coating, more material can be applied locally in the regions in which there are troughs in the surface structure of the workpiece and less material can be applied locally in the regions in which there are higher or protruding structures. As a result, even relatively large fluctuations in surface dimensions on a surface of a workpiece to be coated can be largely evened out, with it also being possible to set a desired defined surface contour of the coated surface.

By means of the method according to the invention, workpieces can be processed in which the surface to be coated needs to be pre-processed less precisely. By means of a differentiated deposition of material, the consumption of coating material and the effort involved in the coating can also be reduced.

In addition, an effort required for a potential post-processing of the coated surface can be reduced. All of this decreases the manufacturing effort and reduces costs.

Basically, almost any surface contour of the coated surface can be set using the method. According to a method variant of the invention, it is particularly preferable for a substantially level surface to be formed during the coating. This may be desired in particular during the coating of brake discs, such that these discs ensure high concentricity and high braking power during operation right from the start.

The coating can be carried out using a common coating method for applying a metal coating, for example a plasma spraying method, a thermal spraying method or the like. It is particularly preferable for the coating to be carried out by laser deposition welding. Particularly robust and stable coatings can be produced as a result.

According to a development of the invention, it is particularly advantageous for, during laser deposition welding, metal powder to be deposited on the surface to be coated by means of the deposition apparatus and for, by means of a laser, the applied metal powder to be locally melted, with the coating being formed. In the process, the metal powder can be applied to a point to be coated on the workpiece by means of one or more deposition nozzles. At the same time, the applied metal powder can be melted in a targeted manner at this point by means of a laser, and the coating is thus formed. If a measuring laser is used to measure the surface structure, the laser of the coating apparatus can accurately follow the path along which the measuring laser has also been moved over the surface to be coated.

It is particularly preferable here that, during the coating, the quantity of the applied metal powder and/or a power of the laser is controlled by the control apparatus. As a result, a consumption of metal powder and also the energy expenditure of the laser can be set particularly efficiently.

According to a development of the invention, particularly high coating performance is achieved by at least two deposition apparatuses simultaneously depositing a coating on the workpiece. According to the number of deposition apparatuses, the processing time can thus be reduced.

It is particularly preferable here for the workpiece to be disc-shaped or planar and for coating to be carried out on two opposite surfaces. This can compensate for shear forces and in particular also thermal stresses in the workpiece.

Particularly good compensation can be achieved by the deposition apparatuses being directly opposite one another and by the coating being carried out on both sides simultaneously.

Basically, the workpiece can be arranged in any manner during the coating, and in particular the surface to be coated can be arranged horizontally. A particularly advantageous configuration of the method according to the invention consists in that, during the coating, the surface to be coated is oriented approximately in parallel with the gravitational force. In particular when depositing metal powder with simultaneous action of a laser, a workpiece arrangement of this kind has the effect that non-molten metal powder is immediately discharged from the surface to be coated in a downward direction and, in comparison with a horizontal arrangement of the surface, no metal powder or barely any metal powder accumulates on the surface to be coated in an undesired manner.

According to another variant of the method according to the invention, it is provided that, after the coating, the coated surface is measured by means of an output measuring apparatus, with a surface structure being detected. Here, the output measuring apparatus may be the same measuring apparatus as that which is intended for the input measurement or may be a separate measuring apparatus. In particular, the surface structure can be measured both during the input measurement and during the output measurement by means of a measuring laser. In a control apparatus, the surface structure of the uncoated surface can be compared with the surface structure of the coated surface. As a result, a layer thickness can be reliably determined. Possible imperfections or deviations which have occurred during coating can also be determined. By means of the control apparatus, a change of the coating parameters or a maintenance of the coating device comprising the deposition apparatus can be determined or initiated on the basis of these measured values and comparative values.

In order to achieve a particularly dimensionally accurate coated surface, according to a development of the invention, it is provided that material-removing post-processing of the coated surface is carried out, with a material-removing tool being brought to the workpiece depending on the surface structure detected in the output measuring apparatus. By means of a control apparatus, in particular the material-removing tool can be adjusted on the basis of the measured surface structure of the coated surface such that a desired final thickness is provided and such that any potential remaining and undesired differences in level on the coated surface are removed.

It is particularly expedient here for the post-processing to include grinding, honing, lapping and/or polishing. Other machining processes, for example material removal by means of a laser, can likewise be used in principle.

Furthermore, the invention comprises a system for metal-coating at least one surface of a workpiece, wherein the system comprises a measuring apparatus, by means of which a surface structure with peaks and troughs in the surface to be coated is detected, at least one deposition apparatus for depositing a coating, wherein the deposition apparatus can be moved relative to the surface of the workpiece during the coating, and a control apparatus, which is designed to control the deposition apparatus on the basis of the detected surface structure, wherein more material is applied in the region of troughs and less material is applied in the region of peaks.

Using this system, the above-described method can in particular be carried out. The advantages described thereby can be achieved.

In the process, the deposition apparatus is in particular designed for carrying out laser deposition welding.

Advantageously, an output measuring apparatus is provided, by means of which a surface structure of the coated surface can be detected. The output measuring apparatus is in particular arranged separately from the input measuring apparatus. The applied layer thickness can, for example, be determined by means of a control apparatus which is connected both to the measuring apparatus for the input measurement and to the output measuring apparatus.

Another preferred embodiment of the system according to the invention consists in that a post-processing station comprising at least one material-removing processing device is arranged. The material-removing processing device may in particular be a grinding device here.

The invention is explained in greater detail in the following on the basis of preferred embodiments shown schematically in the drawings, in which:

FIG. 1 is a schematic view of a system according to the invention;

FIG. 2 is a schematic view for coating a workpiece according to the invention;

FIG. 3 is a perspective view of another system according to the invention based on the system according to FIG. 1;

FIG. 4 is a schematic view of a measuring arrangement; and

FIG. 5 is a schematic view of the result of coating according to the invention.

A first embodiment of a system 10 according to the invention is shown in FIG. 1. Said system comprises four coating modules 20, which form a module group 30 in a parallel arrangement beside one another. An input measuring station 40 is arranged upstream of the module group 30, to which station workpieces (not shown here) are conveyed by means of a main conveying apparatus 60. By means of a handling apparatus 32, which is configured in the present embodiment as a multi-axis robot, the workpieces are picked up from the main conveying apparatus 60 and supplied to the box-shaped input measuring station 40.

The workpieces, in particular a surface to be coated, are measured using the measurement apparatus 42 in the input measuring station 40. In this process, a surface structure of the surface to be coated can in particular be detected, with peaks and troughs in the surface in particular being detected and measured.

The measured workpiece can then be transferred out of the input measuring station 40 via the handling apparatus 32, or directly out of the input measuring station 40, to a linear conveying apparatus 36 which runs along the coating modules 20. A supply apparatus 38 is arranged on the conveying apparatus 36, designed as a linear conveyor, upstream of each coating module 20, by means of which supply apparatus a workpiece is introduced into an inlet opening 24 in a box-shaped housing 21 of the selected coating module 20.

The coating modules 20 are designed to be the same or substantially the same and comprise a transport frame 22. With this transport frame 22, the coating modules 20 can be moved and relocated by means of an indoor crane or forklift truck. This makes it possible, for example in the event of a capacity change, to add or remove additional coating modules 20 or to replace an existing coating module 20 with a new coating module 20 for repair or maintenance purposes.

In the coating module 20, at least one surface of the workpiece 20 is provided with a metal coating, as will be explained in greater detail in the following in conjunction with FIG. 2. After the coating, the workpiece is guided back through the inlet opening 24 onto the conveying apparatus 36. This can also be carried out by the supply apparatus 38. By means of the conveying apparatus 36, the coated workpiece is transported to a common output measuring station 50, in which the coated surface of the workpiece is measured. After this final measurement in the output measuring station 50 by means of an output measuring apparatus 52, the workpiece is placed back onto the main conveying apparatus 60, by means of which the workpiece can be conveyed to further processing. The workpiece can likewise be transferred from the conveying apparatus 36 into the output measuring station 50 and again to the main conveying apparatus 60 by a handling apparatus 32 in the same way as on the input measuring station 40, but this is not shown in FIG. 1.

The measured values determined in the input measuring station 40 for a specified workpiece are transmitted to a central control apparatus. By means of the control apparatus, the conveying apparatus 36 is also controlled by the respective supply apparatus 38 such that the measured workpiece is guided to a specified coating module 20 of the module group 30. At the same time, the measured values of the specified workpiece are forwarded to the selected or specified coating module 20 by the control apparatus, such that the workpiece can be coated depending on the input measured values. After the coating, the workpiece is measured in the box-shaped output measuring station 50, the determined measured values likewise being forwarded to the central control apparatus and to the data set for the specified workpiece. A comparison of the input measured values and the output measured values as well as the coating parameters can be carried out in the control apparatus in order to determine whether a correct coating has been taken place. If necessary, operating parameters of a coating module 20 can be readjusted by the control apparatus during the coating.

According to FIG. 2, a disc-shaped element can be provided as a workpiece 5 to be coated, in particular a brake disc having one or two surfaces 6 to be coated. The metal coating can be applied by two deposition apparatuses 25, each comprising one coating nozzle 26, by means of plasma coating or laser deposition welding. The coating nozzle 26 is arranged on a carrier 27. In plasma spraying, metal particles are melted in an arc and are applied to the surface 6 at high speed. In deposition welding, coating material, in particular a metal powder, is initially applied and then locally melted by means of a laser. In the process, the coating can be carried out in multiple steps and multiple layers. In particular, the layers can also be applied with different layer thicknesses, different materials and different methods in order to achieve desired properties, in particular in terms of adhesion, abrasion resistance and/or corrosion resistance.

In principle, it is possible to carry out the coating using a coating nozzle 26, which is moved along the surfaces 6 to be coated by means of the carrier 27. In addition to plasma spraying and/or laser deposition welding, other thermal metal coating methods may also be used as alternatives or in combination with one another. As shown in FIG. 2, it is preferable for the coating to be deposited on two surfaces 6 of the disc-shaped workpiece 5 simultaneously by two coating apparatuses 25 which are arranged directly opposite one another.

A development of a system 10 according to the invention comprising a total of three module groups 30, which are each made up of four coating modules 20, is shown in FIG. 3. Here, the individual module groups 30 are designed according to the embodiment in FIG. 1, with an input measuring station 40 and an output measuring station 50 being assigned in each module group 30. The total of three module groups 30 are arranged along a linear main conveying apparatus 60, such that, in this parallel arrangement, workpieces can be processed in parallel in the individual module groups 30 and in the individual processing modules 20. After passing through the respective output measuring station 50, a workpiece which has finished being coated is guided back to the main conveying apparatus 60, by means of which the workpiece is fed to a post-processing station 64.

In the embodiment shown according to FIG. 3, the post-processing station 64 comprises a total of four post-processing devices 66, in particular grinding devices, arranged in parallel. By means of the grinding devices, the at least one coated surface of the workpiece can be processed and ground as a final step. In order to ensure efficient post-processing, the detected measured values for each workpiece can be forwarded to the specified grinding device in the post-processing station 64 which has been selected by the control apparatus for processing the workpiece. Depending on the detected final height of the coated surface of the workpiece, for example, the grinding tool can thus be efficiently advanced towards the workpiece in the respective grinding device.

It can be seen in particular from the embodiment according to FIG. 3 that even for larger increases in capacity that are potentially required, not only individual coating modules 20 but also whole module groups 30 which each comprise a plurality of coating modules 20 and associated input measuring station 40 and output measuring station 50 can be readily added to a total system.

FIG. 4 shows a measuring apparatus 42 comprising two measuring sensors 44 when measuring a workpiece 5 before coating. In this figure, the workpiece 5 is a schematically shown brake disc, which comprises two opposite surfaces 6 to be coated. The opposite sensors 44, which can each be arranged on a carrier of the measuring apparatus 42, can be designed as confocal sensors or triangulation sensors comprising a measuring laser.

The sensor 44 for detecting the surface structure 6 preferably moves precisely over the path along which the deposition apparatus 25 will subsequently move in order to deposit the coating.

In order to further increase the measurement quality, a line scan camera can be arranged which covers a radial region of the surface 6 of the workpiece 5. This measuring arrangement can be provided both in the input measuring station 40 and in the output measuring station 52.

FIG. 5 highly schematically shows part of a workpiece 5 after the coating. The surface 6 of the workpiece 5 to be coated has a surface contour having peaks and troughs, which are shown in an exaggerated manner in FIG. 5. Reference sign 3 denotes a schematic surface contour of a coating if said coating were to be uniformly deposited according to a conventional method. In doing so, the peaks and troughs of the surface 6 to be coated would also become apparent on the coated surface with the surface contour 3.

By means of the method according to the invention, more material can be applied to the surface 6 to be coated in the regions of troughs and less material can be applied in the regions of peaks, such that a coating 7 having a substantially level surface 8 results.

Using the method and system according to the invention, a high-quality coating can thus be deposited in a particularly economical manner. 

1. Method for metal-coating at least one surface (6) of a workpiece (5), in which before coating, a surface structure with peaks and troughs in the surface (6) to be coated is detected by means of a measuring apparatus (42), the coating is carried out by means of at least one deposition apparatus (25), which is moved relative to the surface (6) and coating material is applied in the process, and the deposition apparatus (25) is controlled by a control apparatus on the basis of the detected surface structure, wherein more material is applied in the region of troughs and less material is applied in the region of peaks.
 2. Method according to claim 1, characterized in that a substantially level surface (8) is formed during the coating.
 3. Method according to claim 1, characterized in that the coating is carried out as laser deposition welding.
 4. Method according to claim 3, characterized in that during the laser deposition welding, metal powder is deposited on the surface (6) to be coated by means of the deposition apparatus (25) and in that, by means of a laser, the applied metal powder is locally melted, with the coating (7) being formed.
 5. Method according to claim 4, characterized in that during the coating, the quantity of applied metal powder and/or a power of the laser is controlled by the control apparatus.
 6. Method according to claim 1, characterized in that at least two deposition apparatuses (25) simultaneously deposit a coating (7) on the workpiece (5).
 7. Method according to claim 6, characterized in that the workpiece (5) is disc-shaped or planar and in that a coating is carried out on two opposite surfaces (6).
 8. Method according to claim 7, characterized in that the deposition apparatuses (25) are directly opposite one another and the coating is carried out on both sides simultaneously.
 9. Method according to claim 1, characterized in that during the coating, the surface (6) to be coated is oriented approximately in parallel with the gravitational force.
 10. Method according to claim 1, characterized in that after the coating, the coated surface (6) is measured by means of an output measuring apparatus (52), with a surface structure being detected.
 11. Method according to claim 10, characterized in that material-removing post-processing of the coated surface is carried out, wherein a material-removing tool is brought to the workpiece (5) depending on the surface structure detected in the output measuring apparatus (52).
 12. Method according to claim 11, characterized in that the post-processing includes grinding, honing, lapping and/or polishing.
 13. System for the metal-coating of at least one surface (6) of a workpiece (5), in particular according to a method according to claim 1, comprising a measuring apparatus (42), by means of which a surface structure with peaks and troughs in the surface (6) to be coated is detected, at least one deposition apparatus (25) for depositing a coating, wherein the deposition apparatus (25) can be moved relative to the surface (6) of the workpiece (5) during the coating, and a control apparatus, which is designed to control the deposition apparatus (25) on the basis of the detected surface structure, wherein more material is applied in the region of troughs and less material is applied in the region of peaks.
 14. System according to claim 13, characterized in that an output measuring apparatus (52) is provided, by means of which a surface structure of the coated surface (6) can be detected.
 15. System according to claim 14, characterized in that a post-processing station (64) comprising at least one material-removing processing device (66) is arranged. 